feat: add recipe sorting by name, modified date, and created date

[romainhild]

Overview

Add client-side sorting to the recipes list page. Users can sort by name, last modified date, or creation date. The sort controls must scale gracefully to future sort options without consuming excessive space.
This implement #355.

Scope

• Recipes list page (/ and /directory/*)
• Sorting applies to recipe cards only; directories always stay pinned at the top
• No changes to the recipe detail page, API, or search

Not in scope

• Persisting the selected sort across page loads (no localStorage)
• Sorting inside subdirectories independently (same controls apply to all levels)
• Server-side sort (URL params)
• Sorting the search results dropdown

Disclaimer: The implementation has been done using Claude Code. I made the designs decisions and have reviewed the code.
Specs and implementation plans have been added in docs/